U.S. patent application number 13/600980 was filed with the patent office on 2013-09-26 for defect inspection apparatus and defect inspection method.
This patent application is currently assigned to Kabushiki Kaisha Toshiba. The applicant listed for this patent is Hiroyuki HAYASHI. Invention is credited to Hiroyuki HAYASHI.
Application Number | 20130248705 13/600980 |
Document ID | / |
Family ID | 49210880 |
Filed Date | 2013-09-26 |
United States Patent
Application |
20130248705 |
Kind Code |
A1 |
HAYASHI; Hiroyuki |
September 26, 2013 |
DEFECT INSPECTION APPARATUS AND DEFECT INSPECTION METHOD
Abstract
In accordance with an embodiment, a defect inspection apparatus
includes a charged beam irradiation unit, a detection unit, an
energy filter, and an inspection unit. The charged beam irradiation
unit generates a charged beam and irradiates a sample including a
pattern as an inspection target thereon with the generated charged
beam. The detection unit detects secondary charged particles or
reflected charged particles generated from the sample by
irradiation of the charged beam and outputs a signal. The energy
filter is arranged between the detection unit and the sample to
selectively allow the secondary charged particles or the reflected
charged particles with energy associated with an applied voltage to
pass therethrough. The inspection unit applies voltages different
from each other to the energy filter and outputs information
concerning a defect of the pattern from an intensity difference
between signals obtained under application voltage different from
each other.
Inventors: |
HAYASHI; Hiroyuki;
(Yokkaichi-Shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
HAYASHI; Hiroyuki |
Yokkaichi-Shi |
|
JP |
|
|
Assignee: |
Kabushiki Kaisha Toshiba
Tokyo
JP
|
Family ID: |
49210880 |
Appl. No.: |
13/600980 |
Filed: |
August 31, 2012 |
Current U.S.
Class: |
250/307 ;
250/310 |
Current CPC
Class: |
H01J 37/265 20130101;
H01J 2237/24485 20130101; H01J 37/02 20130101; H01J 2237/2446
20130101; H01J 37/28 20130101; H01J 2237/24564 20130101 |
Class at
Publication: |
250/307 ;
250/310 |
International
Class: |
H01J 37/02 20060101
H01J037/02 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 23, 2012 |
JP |
2012-068060 |
Claims
1. A defect inspection apparatus comprising: a charged beam
irradiation unit configured to generate a charged beam and
irradiate a sample comprising a pattern as an inspection target
thereon with the generated charged beam; a detection unit
configured to detect secondary charged particles or reflected
charged particles generated from the sample by irradiation of the
charged beam and to output a signal; an energy filter located
between the detection unit and the sample, the energy filter being
configured to selectively allow the secondary charged particles or
the reflected charged particles with energy associated with an
applied voltage to pass therethrough; and an inspection unit
configured to apply voltages different from each other to the
energy filter and output information concerning a defect of the
pattern from an intensity difference between signals obtained under
application voltage different from each other.
2. The apparatus of claim 1, wherein a plurality of pairs of the
energy filter and the detection unit are provided, and the
apparatus further comprises a charged particle division unit
configured to divide the secondary particles or the reflected
particles in accordance with the number of pairs and to control
each trajectory in such a manner that the divided charged particles
enter each detection unit.
3. The apparatus of claim 1, wherein the inspection unit is
configured to process the signal, acquire a potential contrast
image in accordance with each of the application voltage different
from each other, create a two-dimensional histogram representing a
frequency of appearance with respect to signal intensity at the
same inspection target position by plotting a gradation value of
the potential contrast image acquired in accordance with each of
the application voltage different from each other, set a defect
determining region based on a preset threshold value in the
two-dimensional histogram, and determine that a defect is present
in the pattern when the signal is included in the defect
determining region.
4. The apparatus of claim 3, wherein, when a defect is determined
to be present in the pattern, the inspection unit is configured to
output information of a coordinate position of a signal belonging
to the defect determining region.
5. The apparatus of claim 1, wherein a plurality of pairs of the
energy filter and the detection unit are provided, and the
apparatus further comprises a trajectory control unit configured to
control a trajectory of the secondary charged particles or the
reflected charged particles in such a manner that the secondary
charge particles or the reflected charged particles enter each
detection unit.
6. The apparatus of claim 1, wherein a trajectory control unit
associated with each pair of the energy filter and the detection
unit is provided.
7. The apparatus of claim 1, wherein the inspection unit is
configured to process the signal, acquire a potential contrast
image in accordance with each of the application voltage different
from each other, create a two-dimensional histogram representing a
frequency of appearance with respect to signal intensity at the
inspection target positions associated with each other in different
cells or dies by plotting a gradation value of the potential
contrast image acquired in accordance with each of the application
voltage different from each other, set a defect determining region
based on a preset threshold value in the two-dimensional histogram,
and determines that a defect is present in the pattern when the
signal is included in the defect determining region.
8. The apparatus of claim 7, wherein, when a defect is determined
to be present in the pattern, the inspection unit is configured to
output information of a coordinate position of a signal belonging
to the defect determining region.
9. The apparatus of claim 1, wherein the detector comprises two
individual detectors arranged in such a manner that respective
detection surfaces thereof face each other to sandwich an optical
axis of the charged beam therebetween.
10. The apparatus of claim 1, wherein the detector comprises three
or more individual detectors which are rotationally symmetrically
arranged around an optical axis of the charged beam.
11. The apparatus of claim 1, wherein the voltages different from
each others are selected from combinations of a positive polarity
and a positive polarity, the positive polarity and 0, the positive
polarity and a negative polarity, 0 and the negative polarity, and
the negative polarity and the negative polarity.
12. The apparatus of claim 1, wherein an aspect ratio of the
pattern is not smaller than 10, and the detector detects charged
particles other than charged particles from a bottom portion
between spaces in the pattern.
13. The apparatus of claim 6, wherein the trajectory control unit
is provided in accordance with each pair of the energy filter and
the detection unit.
14. A defect inspection method comprising: generating a charged
beam and irradiating a sample comprising a pattern thereon as an
inspection target with the charged beam; performing filtering under
filtering conditions different from each other so as to allow
passage of secondary charged particles or reflected charge
particles with desired energy generated from the sample by
irradiation of the charged beam; detecting the secondary charged
particles or the reflected charged particles selected by the
filtering, and outputting a signal; and outputting information
concerning a defect of the pattern from an intensity difference
between signals obtained under the filtering conditions different
from each other.
15. The method of claim 14, wherein the filtering under the
filtering conditions different from each other and the detection
are simultaneously carried out.
16. The method of claim 14, further comprising dividing the
secondary particles or the reflected particles in accordance with
the number of pairs and controlling each trajectory in such a
manner that the divided charged particles enter each detection
unit.
17. The method of claim 14, wherein the performing inspection
comprises: processing the signal to acquire a potential contrast
image in accordance with each of the application voltage different
from each other, creating a two-dimensional histogram representing
a frequency of appearance with respect to signal intensity at the
same inspection target position by plotting a gradation value of
the potential contrast image acquired in accordance with each of
the application voltage different from each other, setting a defect
determining region based on a preset threshold value in the
two-dimensional histogram, and determining that a defect is present
in the pattern when the signal is included in the defect
determining region.
18. The method of claim 17, further comprising, when a defect is
determined to be present in the pattern, outputting information of
a coordinate position of a signal belonging to the defect
determining region.
19. The method of claim 14, wherein the performing inspection
comprises: processing the signal, acquire a potential contrast
image in accordance with each of the application voltage different
from each other, creating a two-dimensional histogram representing
a frequency of appearance with respect to signal intensity at the
inspection target positions associated with each other in different
cells or dies by plotting a gradation value of the potential
contrast image acquired in accordance with each of the application
voltage different from each other, setting a defect determining
region based on a preset threshold value in the two-dimensional
histogram, and determining that a defect is present in the pattern
when the signal is included in the defect determining region.
20. The method of claim 19, wherein the performing inspection
comprises, when a defect is determined to be present in the
pattern, outputting information of a coordinate position of a
signal belonging to the defect determining region.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is based upon and claims the benefit of
priority from the prior Japanese Patent Application No.
2012-068060, filed on Mar. 23, 2012, the entire contents of which
are incorporated herein by reference.
FIELD
[0002] Embodiments described herein relate generally to a defect
inspection apparatus and a defect inspection method.
BACKGROUND
[0003] In recent years, an aspect ratio of a pattern is increased
with advancement of integration degrees of semiconductor devices. A
conventional defect inspection apparatus using an electron beam
cannot detect an electrical short circuit that is present, for
example, on a bottom between wiring lines, in a high-aspect
structure.
BRIEF DESCRIPTION OF THE DRAWINGS
[0004] FIG. 1 is a block diagram showing an outline configuration
of a defect inspection apparatus according to Embodiment 1;
[0005] FIG. 2 is an explanatory view of a defect inspection method
according to Embodiment 1;
[0006] FIG. 3 is a view showing each example of a trajectory of
secondary electrons/reflected electrons and an obtained potential
contrast image when an energy filter is turned on;
[0007] FIG. 4 is a view showing each example of a trajectory of the
secondary electrons/reflected electrons and a potential contract
image obtained from the same inspecting position as that in FIG. 3
when the energy filter is turned off;
[0008] FIG. 5 is a view showing an example of a difference image of
the potential contrast image;
[0009] FIG. 6 is a schematic view of a histogram showing a
frequency of appearance of the potential contrast images in FIG. 3
and FIG. 4 with respect to signal intensity;
[0010] FIG. 7 is a flowchart showing an outline procedure of the
defect inspection method according to Embodiment 1;
[0011] FIG. 8 is a view showing each example of a trajectory of
secondary electrons/reflected electrons and an obtained potential
contrast image when an energy filter is turned on;
[0012] FIG. 9 is a view showing each example of a trajectory of the
secondary electrons/reflected electrons and a potential contrast
image obtained from an inspecting position corresponding to the
inspecting position in FIG. 8 when the energy filter is turned
off;
[0013] FIG. 10 is a view showing another example of a difference
image of the potential contrast image; and
[0014] FIG. 11 is a flowchart showing an outline procedure of a
defect inspection method according to Embodiment 2.
DETAILED DESCRIPTION
[0015] In accordance with an embodiment, a defect inspection
apparatus includes a charged beam irradiation unit, a detection
unit, an energy filter, and an inspection unit. The charged beam
irradiation unit is configured to generate a charged beam and
irradiate a sample including a pattern as an inspection target
thereon with the generated charged beam. The detection unit is
configured to detect secondary charged particles or reflected
charged particles generated from the sample by irradiation of the
charged beam and to output a signal; The energy filter is arranged
between the detection unit and the sample and configured to
selectively allow the secondary charged particles or the reflected
charged particles with energy associated with an applied voltage to
pass therethrough; The inspection unit is configured to apply
voltages different from each other to the energy filter and to
output information concerning a defect of the pattern from an
intensity difference between signals obtained under application
voltage different from each other.
[0016] Embodiments will now be explained with reference to the
accompanying drawings. Like components are provided with like
reference signs throughout the drawings and repeated descriptions
thereof are appropriately omitted.
(A) Embodiment 1
(1) Defect Inspection Apparatus
[0017] FIG. 1 is a block diagram showing an outline configuration
of a defect inspection apparatus according to Embodiment 1.
[0018] The defect inspection apparatus according to the present
embodiment includes a filament electrode 1, a condenser lens 4,
beam scan deflectors 7a and 7b, an objective lens 9, a stage 19, a
Wien filter 8, energy filters EF10 and EF20, individual secondary
electron/reflected electron detectors 12 and 13, variable
direct-current power supplies 14 and 15, a signal processing unit
21, an image processing unit 23, a control computer 22, a memory
MR, and a display unit 24.
[0019] A semiconductor substrate S is mounted on an upper surface
of the stage 19, and the stage 19 receives a control signal from
the control computer 22 and moves the semiconductor substrate S in
a horizontal direction and a vertical direction. On a surface of
the semiconductor substrate S, wiring lines WR1, WR2 . . . (see
FIG. 3 and FIG. 9) as measurement targets are formed at a
predetermined pitch in accordance with each die or each chip. In
this embodiment, an aspect ratio of the wiring lines WR1 and WR2 is
not smaller than 10. In this embodiment the wiring lines are taken
for instance as inspection target patterns, but a pattern of
rectangular or circular holes aligned in one predetermined
direction or two directions orthogonal to each other can also be
inspected besides such a line-and-space pattern. The semiconductor
substrate S corresponds to, e.g., a sample in this embodiment. The
stage 19 is connected to a ground potential (GND) in this
embodiment. The filament electrode 1 generates an electron beam EB
and applies it toward the semiconductor substrate S. In the present
embodiment, the electron beam EB corresponds to, e.g., a charged
beam, and the filament electrode 1 corresponds to, e.g., a charged
beam irradiation unit.
[0020] The condenser lens 4 generates a magnetic field or an
electric field and condenses the electron beam EB so that an
appropriate beam flux can be obtained. The objective lens 9
generates, a magnetic field or an electric field and again
converges the electron beam EB so that the semiconductor substrate
S can be irradiated with the electron beam EB in an in-focus
state.
[0021] The beam scan deflectors 7a and 7b are connected to the
control computer 22, generate a magnetic field or an electric field
used for deflecting the electron beam EB in accordance with a
control signal supplied from the control computer 22, whereby the
semiconductor substrate S is two-dimensionally scanned with the
electron beam EB. The individual secondary electron/reflected
electron detectors 12 and 13 are arranged in such a manner that
their detection surfaces face each other so as to sandwich an
optical axis of the electron beam EB at the same height from the
semiconductor substrate S in this embodiment. The individual
secondary electron/reflected electron detectors 12 and 13 detect
secondary electrons or reflected electrons (which will be simply
referred to as "secondary electrons/reflected electrons"
hereinafter) generated from the semiconductor substrate S by
irradiation of the electron beam EB, output signals, and supply
them to the signal processing unit 21. In the present embodiment,
the secondary electron/reflected electron corresponds to, e.g., a
secondary charge particle or a reflected charged particle. The Wien
filter 8 is connected to the control computer 22, allows the
electron beam EB that passes through the condenser lens 4 and the
like and is applied to the semiconductor substrate S to pass
therethrough without changing a trajectory, and bends a trajectory
of the secondary electrons/reflected electrons generated from the
semiconductor substrate S in such a manner that the secondary
electrons/reflected electrons travel toward the respective
detection surfaces of the individual secondary electron/reflected
electron detectors 12 and 13. In the present embodiment, the Wien
filter 8 also functions as a beam splitter, and it divides the
secondary electrons/reflected electrons in such a manner that
substantially the same amounts of the secondary electrons/reflected
electrons from the semiconductor substrate S can travel toward the
respective individual secondary electron/reflected electron
detectors 12 and 13 in accordance with a control signal supplied
from the control computer 22. In the present embodiment, the Wien
filter 8 corresponds to, e.g., a charged particle division
unit.
[0022] The energy filters EF10 and EF20 are arranged between the
individual secondary electron/reflected electron detectors 12 and
13 and the Wien filter 8, and they filter and selectively allow the
secondary electrons/reflected electrons to pass therethrough so
that the secondary electrons/reflected electrons having desired
energy can enter the respective detection surfaces of the
individual secondary electron/reflected electron detectors 12 and
13.
[0023] The energy filters EF10 and EF20 are connected to the
variable direct-current power supplies 14 and 15.
[0024] A level of energy that allows filtering is determined in
dependence on values of voltages applied from the variable
direct-current power supplies 14 and 15. The variable
direct-current power supplies 14 and 15 are connected to the
control computer 22 and apply voltages to the energy filters EF10
and EF20. The values of the voltages applied to the energy filters
EF10 and EF20 are determined in accordance with a control signal
supplied from the control computer 22. In this embodiment, values
of the voltages applied to the individual secondary
electron/reflected electron detectors 12 and 13 correspond to,
e.g., application voltage conditions different from each other and
filtering conditions different from each other. Further, a pair of
the energy filter EF10 and of the individual secondary
electron/reflected electron detector 12 and a pair of the energy
filter EF20 and of the individual secondary electron/reflected
electron detector 13 correspond to, e.g., a plurality of pairs of
an energy filter and a detection unit in the present embodiment.
The signal processing unit 21 individually process signals supplied
from the individual secondary electron/reflected electron detectors
12 and 13 in accordance with a control signal fed from the control
computer 22 and creates a contrast image which reflects a potential
distribution on the surface of the semiconductor substrate S (which
will be referred to as a "potential contrast image" hereinafter).
Information of coordinate positions of a corresponding inspection
target region is given to data of the potential contrast image in
accordance with each pixel. In this embodiment, in regard to the
same inspection target region in the surface of the semiconductor
substrate S, obtained are two images, i.e., a potential contrast
image based on a signal from the individual secondary
electron/reflected electron detector 12 and a potential contrast
image based on a signal from the individual secondary
electron/reflected electron detector 13.
[0025] The image processing unit 23 executes arithmetic processing
with respect to the potential contrast image supplied from the
signal processing unit 21, creates a difference image, also creates
a later-described two-dimensional histogram, and makes a defect
judgment in accordance with a control signal supplied from the
control computer 22. The created potential contrast image, the
difference image, and a defect judgment result are displayed by a
display unit 24 such as a liquid crystal display.
[0026] The memory MR stores an inspection recipe in which a
specific procedure of the defect inspection is written. The control
computer 22 reads out the inspection recipe from the memory MR,
creates the various control signals, and supplies them to the beam
scan deflectors 7a and 7b, the Wien filter 8, the variable
direct-current power supplies 14 and 15, the signal processing unit
21, and the image processing units 23 and 24.
[0027] In the present embodiment, the signal processing unit 21,
the control computer 22, and the image processing unit 23
correspond to, e.g., an inspection unit.
[0028] A defect inspection using the defect inspection apparatus
shown in FIG. 1 will now be described with reference to FIG. 2 to
FIG. 6.
[0029] First, values of the voltages applied to the energy filters
EF10 and EF20 are set. In this embodiment, a direct-current voltage
DC=-40 V is applied to the energy filter EF10, and a direct-current
voltage DC=0 V is applied to the energy filter EF20, in other
words, no voltage application is set for the energy filter
EF20.
[0030] The values of the voltages applied to the energy filters
EF10 and EF20 are not restricted to these values, they are
appropriately determined in accordance with a material of a matter
that forms a base substance of a sample, a material, a shape, an
aspect ratio, a degree of coarseness and fineness of a pattern that
is an inspection target, or a material of a peripheral pattern, and
they can be different from each other in such a manner that a
difference can be confirmed in a potential contrast image (see FIG.
3 to FIG. 5). Therefore, as polarities of the application voltages,
there can be combinations of the positive polarity and the positive
polarity, the positive polarity and 0, the positive polarity and
the negative polarity, 0 and the negative polarity, and the
negative polarity and the negative polarity.
[0031] Then, the semiconductor substrate S having the wiring lines
WR1 as an inspection target formed thereon is mounted on the stage
19. A defect type that should be detected in this embodiment is an
electrical short circuit defect that is present on a bottom surface
of a space region between the wiring lines WR1 having a high aspect
ratio. Subsequently, the variable direct-current power supply 14
changes the direct-current voltage applied to the energy filter
EF10 from DC=0 V to DC=-40 V in accordance with a control signal
supplied from the control computer 22, whereby the energy filter
EF10 is turned on. On the other hand, since the voltage applied to
the energy filter EF20 remains as 0, the energy EF20 is maintained
in an OFF state.
[0032] In this state, the electron beam EB is emitted from the
filament electrode 1, the stage 19 is moved as indicated by arrows
in FIG. 2, and the electron beam EB is deflected by the beam scan
deflectors 7a and 7b while bringing an inspection target region
into view, whereby the inspection target region including the
wiring line WR1 is scanned by the electron beam EB. As indicated by
broken lines in FIG. 2, secondary electrons/reflected electrons
generated from the semiconductor substrate S are divided into two
by the Wien filter 8, respective trajectories are bent, and the
secondary electrons/reflected electrons travel toward the detection
surfaces of the individual secondary electron/reflected electron
detectors 12 and 13.
[0033] The energy filters EF10 and EF20 are disposed on the front
sides of the respective individual secondary electron/reflected
electron detectors 12 and 13, and the secondary electrons/reflected
electrons are filtered by these members. Since the energy filter
EF20 is OFF, as shown in FIG. 4, it allows the incoming secondary
electrons/reflected electrons SEall having high energy and low
energy to pass therethrough and to enter the individual secondary
electron/reflected electron detector 13. Since the secondary
electrons/reflected electrons SEhigh having high energy are
generated from a top surface, especially an edge portion of the
wiring line WR1, these electrons appear as a bright spot (bright)
in an obtained contrast image as shown in Img 10B in FIG. 4. On the
other hand, the secondary electrons/reflected electrons SElow
having low energy are generated from the space region between the
wiring lines WR1, and they appear as a dark spot (dark) in the
potential contrast image.
[0034] However, as indicated by reference marks DF10 and DF11 in
FIG. 4, short circuit defects DF10 and DF11 are formed on a bottom
portion of the space between WR1 in inspection target regions, the
high-energy secondary electrons/reflected electrons SEhigh are also
generated from top surfaces of these portions, but few defects can
exceeds sidewalls of the wiring lines WR1 because of a height of
the aspect ratio, and an amount of the low-energy secondary
electrons/reflected electrons SElow generated from the wiring
bottom is overwhelmingly large in particular. Since the energy
filter EF20 is OFF, the secondary electrons/reflected electrons
SEall having the high energy and the low energy are detected by the
individual secondary electron/reflected electron detector 13, and
hence a defective portion does not appear in the potential contrast
image Img 10B. The potential contrast image obtained when the
energy filter is OFF will be referred to as a "reference image"
hereinafter.
[0035] On the other hand, since the energy filter EF10 is ON, as
shown in FIG. 3, the low-energy secondary electrons/reflected
electrons SElow are blocked by the energy filter EF10, and they
cannot enter the individual secondary electron/reflected electron
detector 12. As a result, a majority of the secondary
electrons/reflected electrons is not detected from the space region
between the wiring lines WR1, especially the bottom portion.
Further, the high-energy secondary electrons/reflected electrons
SEhigh pass through the filter EF10 and enter the detection surface
of the individual secondary electron/reflected electron detector
12. Therefore, not only the secondary electrons/reflected electrons
from the top surface of the wiring line WR1 but also the secondary
electrons/reflected electrons from the top surfaces of the short
circuit defects DF10 and DF11 are detected as a part of the
high-energy secondary electrons/reflected electrons SEhigh. As a
result, as shown in FIG. 3, the defects clearly appear in the
potential contrast image Img 10A. The potential contrast image
obtained when the energy filter is ON will be referred to as a
"defect candidate image" hereinafter.
[0036] In the example depicted in FIG. 3, signal intensity of a
region P25 associated with the wiring line WR1 has 120 gradations,
and signal intensity of the short circuit defects DF10 and DF11
also has 120 gradations. Furthermore, in the example shown in FIG.
4, signal intensity of a region P27 associated with the wiring line
WR1 has 150 gradations, and signal intensity of a region P28
associated with the bottom of the space between the wiring lines
WR1 has 30 gradations.
[0037] As shown in FIG. 5, the image processing unit 23 creates a
difference image Img (10A-10B) of the defect candidate image Img
10A and the reference image Img 10B based on arithmetic processing
and thereby determines whether the defects DF10 and DF11 are
present. Moreover, the image processing unit 23 also creates a
two-dimensional histogram showing a frequency of appearance of each
of the defect candidate image Img 10A and the reference image Img
10B with respect to the signal intensity, sets a defect determining
region in the two-dimensional histogram based on a preset threshold
value (a reference value), and thereby determines whether an
electrical short circuit defect is present on the bottom surface of
the space between the wiring lines WR1. FIG. 6 shows an example of
the two-dimensional histogram obtained in relation to the defect
candidate image Img 10A and the reference image Img 10. In the
example of FIG. 6, the 30 gradations as the signal intensity from
the space between the wiring lines WR1 detected when the energy
filter EF20 is OFF are set as a threshold value, and regions
defined based on this threshold value are set as defect determining
regions RD1 and RD2. The image processing unit 23 determines a
position at which a signal belonging to the defect determining
region RD1 or RD2 as a defective position, and outputs the signal
together with its coordinate position. Giving a more specific
description, in the defect candidate image Img 10A and the
reference image Img 10, a difference of the signal intensity on the
wiring surfaces is as small as 30 gradations and, on other hand, a
difference of the signal intensity at wiring short circuit
positions is as large as 90 gradations. Therefore, when a reference
value (a threshold value) used for determining a defect is set to
30, whether an electrical short circuit is present between the
wiring lines WR1 in the high-aspect configuration can be
determined.
[0038] As described above, according to the defect inspection
apparatus of this embodiment, the apparatus includes the Wien
filter 8 that divides the secondary electrons/reflected electrons
generated from the same inspection target region from each other
and allows these electrons to enter the individual secondary
electron/reflected electron detectors 12 and 13 through the two
energy filters EF10 and EF20 having voltages meeting different
conditions applied thereto. Whether a defect is present is
determined based on an intensity difference between signals
obtained under different application voltage conditions, thereby
enabling the defect inspection of the same wiring line in the same
die at the same position. As a result, an influence of noise caused
due to displacement or vibration of the stage 19, defocus of the
electron beam EB, or charging due to repeated application of the
electron beam EB to the same position can be eliminated, and hence
the inspection can be highly accurately carried out.
(2) Defect Inspection Method
[0039] A defect inspection method according to Embodiment 1 will
now be described with reference to FIG. 7. FIG. 7 is a flowchart
showing an outline procedure of a defect inspection method
according to the present embodiment.
[0040] First, conditions for filtering secondary
electrons/reflected electrons generated from the surface of the
semiconductor substrate S having the wiring line WR1 as an
inspection target are set. In this embodiment, to divide the
generated secondary electrons/reflected electrons by the Wien
filter 8 and detect these electrons by the two individual secondary
electron/reflected electron detectors 12 and 13, different
filtering conditions are set (a step S10).
[0041] Here, values of voltages applied to the energy filters EF10
and EF20 are determined as filtering conditions, one is set as
DC=-40 V, and the other is set as DC=0 V. Subsequently, the
semiconductor substrate S is mounted on the stage 19 of the defect
inspection apparatus, and the electron beam EB is generated, and
the inspection target region is scanned (a step S20).
[0042] Then, of the secondary electrons/reflected electrons
generated from the inspection target region, in regard to one
divided by the Wien filter 8, DC=-40 V is applied to the energy
filter EF10 to turn on the energy filter EF10 (a step S31), and a
signal obtained by detecting the high-energy secondary
electrons/reflected electrons SEhigh selected by filtering is
processed to acquire the defect candidate image Img 10A (a step
S32). Additionally, of the secondary electrons/reflected electrons
generated from the inspection target position, in regard to the
other divided by the Wien filter 8, a voltage applied to the energy
filter EF20 is set to DC=0V, the energy filter EF20 is turned off
(a step S51), and a signal obtained by detecting the high-energy
and low-energy secondary electrons/reflected electrons SEall is
processed to acquire the reference image Img 10B (a step S52).
[0043] The procedures of the steps S31 to S52 can be simultaneously
processed in parallel if the defect inspection apparatus depicted
in FIG. 1 is used. However, it is to be noted that the procedures
of the steps S31 and S32 may first be processed and then the
control may advance to the procedures of the steps S51 and S52 as
shown in the flowchart of FIG. 11.
[0044] Subsequently, a two-dimensional histogram is created from
the defect candidate image Img 10A obtained when the energy filter
EF10 is ON (DC=-40 is applied) and the reference image Img 10B
obtained when the energy filter EF20 is OFF (DC=0V is applied) (a
step S60).
[0045] Then, in the created two-dimensional histogram, a reference
value (a threshold value) used for judging a defect is determined,
the defect determining regions RD1 and RD2 based on this value are
set, and whether the electrical short circuit defects DF10 and DF11
are present on the bottom surface of the space between the wiring
lines is determined (a step S70).
[0046] At last, when it is determined that the defects are present,
coordinates of their positions are extracted and output (a step
S80).
(B) Embodiment 2
[0047] For a cell-to-cell image comparison inspection system and a
die-to-die image comparison inspection system which are used for
general defect inspection techniques, when it is determined that
defects are present at corresponding positions in both an
inspection image and a reference image, e.g., when many defects are
present on a semiconductor substrate, a difference may not be
detected from the image comparison, and hence "no defect" may be
determined even though defects are actually present.
[0048] In the present embodiment, respective potential contrast
images are acquired under filtering conditions which differ
depending on each of corresponding cells or dies, and a difference
image of the two obtained potential contrast images is created,
thereby realizing highly accurate detection of a defect.
(1) Defect Inspection Apparatus
[0049] For the present embodiment, the defect inspection apparatus
shown in FIG. 1 can also be used. However, in the present
embodiment filtering conditions that differ depending on each of
corresponding cells or dies are used. Thus, functions of the Wien
filter 8 as a beam splitter is not used, and a direction of bending
secondary electrons/reflected electrons is changed depending on
acquisition of a defect candidate image and acquisition of a
reference image. Therefore, in place of the Wien filter 8, two Wien
filters (not shown) may be arranged between energy filters EF10 and
EF20 and a semiconductor substrate S, respectively.
[0050] First, like Embodiment 1, a voltage DC=-40 V is applied to
the energy filter EF10 to turn on the energy filter EF10, and a
voltage DC=0 V is applied to the energy filter EF20 to keep the
energy filter EF20 in an OFF state. In this state, first, as shown
in FIG. 8, an electron beam EB is applied to a wiring line WR1 in
an inspection target region on the semiconductor substrate S. A
trajectory of secondary electrons/reflected electrons generated
from the surface of the semiconductor substrate S is controlled by
the Wien filter 8 in such a manner that the secondary
electrons/reflected electrons can travel toward the energy filter
EF10. Since the energy filter EF10 is ON, low-energy secondary
electrons/reflected electrons SElow are blocked, and a majority of
these electrons is not detected by an individual secondary
electron/reflected electron detector 12. On the other hand, since
high-energy secondary electrons/reflected electrons SEhigh pass
through the energy filter EF10, they are detected by the individual
secondary electron/reflected electron detector 12. Thus, defects
DF10 and DF11 appear in an obtained defect candidate image Img
10A.
[0051] Then, the semiconductor substrate S is moved by a stage 19,
and the electron beam EB is applied to a wiring line WR2 of a cell
or a die associated with a cell or a die in the inspection target
region on the semiconductor substrate S, which is typically an
adjacent cell or die. Furthermore, a trajectory of the secondary
electrons/reflected electrons generated from the surface of the
semiconductor substrate S is controlled by the Wien filter 8 in
such a manner that the secondary electrons/reflected electrons can
travel toward the energy filter EF20. Since the energy filter EF 20
is OFF, the high-energy or low-energy secondary electrons/reflected
electrons SEall pass through the energy filter EF20, and they are
detected by the individual secondary electron/reflected electron
detector 13. Although defects DF20 and DF21 are actually present on
the wiring line WR2 in analogous with the inspection target region,
the defects do not appear in an obtained reference image Img
20B.
[0052] Therefore, as shown in FIG. 10, like Embodiment 1, when the
image processing unit 23 acquires a difference image Img (10A-10B)
of the defect candidate image Img 10A and the reference image Img
20B, the defects DF10 and DF11 can be specified.
(2) Defect Inspection Method
[0053] A defect inspection method according to the present
embodiment will now be described with reference to a flowchart of
FIG. 11.
[0054] First, conditions for filtering secondary
electrons/reflected electrons generated from the surface of the
semiconductor substrate S having the wiring lines WR1 and WR2 as
inspection targets are set. In this embodiment, filtering
conditions that differ depending on acquisition of the defect
candidate image Img 10A and acquisition of the reference image Img
20B are set (a step S10). Here, values of voltages applied to the
energy filters 12 and 13 are determined as filtering conditions,
one of the voltage is determined as DC=-40 V, and the other of the
same is determined as DC=0 V.
[0055] Subsequently, the semiconductor substrate S is mounted on
the stage 19 of the defect inspection apparatus, and the electron
beam EB is generated to scan the inspection target region (a step
S20). Further, DC=-40 V is applied to the energy filter EF10 to
turn on the energy filter EF10 (a step S31), and a trajectory of
the secondary electrons/reflected electrons generated from the
inspection target position is controlled by the Wien filter 8 in
such a manner that the secondary electrons/reflected electrons can
travel toward the energy filter EF10. Since the energy filter EF 10
is ON, the high-energy secondary electrons/reflected electrons
SEhigh are selectively detected by filtering, and an obtained
signal is processed to acquire the defect candidate image Img 10A
(a step S32).
[0056] Then, the stage is moved, and the electron beam EB is
applied to the wiring line WR2 on a cell or a die in a reference
region adjacent to a cell or die in the inspection target region (a
step S40).
[0057] Moreover, DC=0 V is applied to the energy filter EF20 to
turn off the energy filter EF20 (a step S51), the high-energy and
low-energy secondary electrons/reflected electrons SEall are
detected, and an obtained signal is processed to acquire the
reference image Img 20B (a step S52).
[0058] Subsequently, a two-dimensional histogram is created from
the defect candidate image Img 10A obtained by the energy filter in
the ON state (DC=-40 V is applied) and the reference image Img 20B
obtained by the energy filter in the OFF state (DC=0 V is applied)
(a step S60).
[0059] Then, in the created two-dimensional histogram, a reference
value (a threshold value) for judging a defect is determined, and
defect determining regions RD1 and RD2 based on this value are set,
whereby whether electrical short circuit defects DF10 and DF11 are
present on the bottom surface of the space between the wiring lines
is determined (a step S70).
[0060] At last, when the defects are determined to be present,
coordinates of their positions are extracted and output (a step
S80).
[0061] As described above, according to Embodiment 2, even if many
defects are present on the semiconductor substrate, the defects can
be highly accurately detected.
[0062] According to the defect inspection apparatus of at least one
embodiment described above, since different direct-current voltages
are applied to the energy filters EF10 and EF20 from the variable
direct-current power supplies 14 and 15, and the image processing
unit 23 that determines, e.g., presence/absence of defects from an
intensity difference between signals obtained from the individual
secondary electron/reflected electron detectors 12 and 13 is
provided, thereby inspecting a pattern in a high-aspect
configuration with high accuracy.
[0063] Moreover, according to the defect inspection method of at
least one embodiment described above, since performing inspection
includes outputting information concerning defects of a pattern as
an inspection target from an intensity difference between signals
obtained under filtering conditions which are different from each
other, a pattern in a high-aspect configuration can be highly
accurately inspected.
[0064] Although the several embodiments according to the present
inventions have been described, these embodiments have been
presented as examples, and they do not intend to limit the scope of
the inventions.
[0065] For example, in the foregoing embodiments, the description
has been given as to the individual secondary electron/reflected
electron detectors 12 and 13 that are arranged in such a manner
that their detection surfaces face each other so as to sandwich an
optical axis of the electron beam EB at the same height from the
semiconductor substrate S. However, the number and the arrangement
conformation of the individual secondary electron/reflected
electron detectors are not restricted to those in the above
conformation. In accordance with types of defects as detection
targets, three or more individual secondary electron/reflected
electron detectors may be e.g., rotationally symmetrically arranged
around an optical axis. In contrast, a dome-like omnidirectional
detector may be further provided and the Wien filter 8 may divide
the secondary electrons/reflected electrons in such a manner that
an amount of the secondary electrons/reflected electrons can be
equivalent in respective directions.
[0066] Additionally, although the electrical short circuit defects
DF10, DF11, DF20, and DF21 have been described as the inspection
target defects, the present inventions are not restricted thereto,
and contamination that is deposited in the space between the wiring
lines may also be an inspection target, as long as the high-energy
secondary electrons/reflected electrons are generated by
irradiation of the electron beam EB, for example.
[0067] While certain embodiments have been described, these
embodiments have been presented by way of example only, and are not
intended to limit the scope of the inventions. Indeed, the novel
methods and systems described herein may be embodied in a variety
of other forms; furthermore, various omissions, substitutions and
changes in the form of the methods and systems described herein may
be made without departing from the spirit of the inventions. The
accompanying claims and their equivalents are intended to cover
such forms or modifications as would fall within the scope and
spirit of the inventions.
* * * * *